Water-in-oil emulsion explosives are now well known in the explosives art. Bluhm, in U.S. Patent No. 3,447,978, disclosed a composition comprising an aqueous discontinuous phase containing dissolved Oxygen-supplying salts, a carbonaceous fuel continuous phase, an occluded gas and a water-in-oil emulsifier. Cattermole et al, in U.S. Pat. No. 3,674,578, describe a similar composition containing as part of the inorganic oxidizer phase, nitrogen-base salt such as an amine nitrate. Tomic, in U.S. Pat. No. 3,77,522 also describes a similar composition wherein the surfactant is an alkali or ammonium stearate. Wade, in U.S. Pat. No. 3,715,247 describes a small-diameter cap-sensitive emulsion type explosive composition comprising carbonaceous fuel, water, inorganic salts, an emulsifier, gas bubbles, and a detonation catalyst consisting of water-soluble salt containing selected metals. In U.S. Pat. No. 3,765,964, Wade describes an improvement in the composition of U.S. Pat. No. 3,715,247 by including therein a water-soluble strontium compound to provide further sensitivity. Wade again, in U.S. Pat. No. 4,110,134, describes an emulsion type explosive composition devoid of any self explosive ingredient and containing a closed-cell void-containing material as a density controller. Wade further describes, in U.S. Pat. No, 4,149,916, a cap sensitive emulsion type explosive composition containing perchlorates and occluded air and in U.S. Pat. No. 4,149,917, he describes a similar composition without any sensitizer other than occluded air. Sudweeks and Jessop in U.S. Pat. No. 4,141,767, describe a cap-insensitive water-in-oil emulsion explosive composition containing a fatty acid amine or ammonium salt surfactant having a chain length ranging from 14 to 22 carbon atoms. In Canadian Pat. No. 1,096,173, there is described a sensitive emulsion type explosive composition containing fuel, water, salts, gas bubbles, an emulsifier and an emulsification promoter comprising a highly chlorinated paraffinic hydrocarbon. Clay, in U.S. Pat. No. 4,111,727, describes a blasting composition consisting of a greasy, water-in-oil emulsion admixed with a substantially undissolved particulate solid oxidizer salt constituent so as to fill the interstices between salt particles to increase the bulk density of the mass. Similar blasting compositions had also been disclosed by Egly and Neckar in U.S. Pat. No. 3,161,551 and by Butterworth in South African Pat. Specification No. 71/3355.
The compositions of Wade, and other prior art water-in-oil emulsion-based explosives exhibit limited stability. These compositions tend to break down when exposed to shear conditions within a pump or to become dry and hard upon aging which conditions deleteriously affects their handling characteristics and their explosive performance. The surfactants used heretofore have not been sufficiently effective in permanently suppressing the coalescence of the supersaturated oxidizer salt droplets. Fairly large quantities of perchlorate salts on other sensitizing agents often must be incorporated in the mixtures in order to retain cap-sensitivity at densities above 1.10 g/cc for any appreciable period of time. Any of the composition containing added excess salts would exhibit very limited stability because of the seeding or precipitation effect of the salt crystals leading to a fairly rapid breakdown of the emulsion.
The effectiveness of emulsification of the aqueous salts and liquid fuels as a promoter of explosive performance is crucially dependent on the activity of the surfactant chosen. The surfactant aids the process of droplets subdivision and dispersion in the continuous phase by reducing the surface tension and the energy required to create new surfaces. The surfactant also reduces the rate of coalescence by coating the surface of the droplets with a molecular layer of material. The surfactants employed in the aforementioned prior art explosive compositions are somewhat effective in performing these function but they are limited in their utility because coalescence of the droplets and breakdown of the emulsion takes place under shear conditions and over time.
Proposals have been made to improve the stability of water-in-oil emulsion explosives by employing particular surfactants which function to a high level of efficiency in the harsh environment of an oxidizer salt solution. In U.S. Pat. No. 4,357,184 (Binet et al), it is disclosed that a combination of a conventional surfactant and an amphiphatic synthetic polymeric surfactant will lead to enhanced explosives stability. In United Kingdom Pat. Specification No. 2,156,799A, the use is proposed of a surfactant comprising a compound which contains a polyalk(en)yl succinic anhydride residue hydrophobic component. In U.S Pat. No. 4,708,753, an explosive emulsion is claimed wherein the surfactant is a salt derived from a substituted carboxylic acid and an amine. In published South African Specification No. 87/8540, an explosive emulsion is claimed in which the surfactant is derived from a carboxylic acylating agent, a polyamine and an acid. In U.S. Pat. No. 4,784,706 the emulsifier is a derivatized polybutyl or polypropyl phenol.